Icons are easier to scan than raw numbers
Something like a goal-completion rate or inventory status is hard to judge at a glance from numbers alone. Attaching a traffic-light or arrow icon makes it much more intuitive to see good, average, and poor status without reading every value.
Combine icon sets with other conditional formatting styles
Icon sets sit alongside two related tools in the same menu -- data bars, which show relative size as an in-cell bar, and color scales, which shade cells along a gradient. It's worth trying each on the same data, since sometimes a color scale communicates a trend better than discrete icons, or vice versa. Also note that for metrics where a lower number is better, you can reverse the icon order in Manage Rules so a low value still shows green.
Frequently Asked Questions
Can I show only the icons and hide the numbers?
Yes -- checking "Show Icon Only" in Manage Rules hides the numeric value and displays just the icon in the cell.
How many icon set styles are there?
Excel includes a range of built-in styles -- traffic lights, arrows, stars, shapes, and more -- with three-, four-, and five-level versions of most of them.